Low pressure vapor phase deposition of organic thin films

ABSTRACT

Methods for preparing organic thin films on substrates, the method comprising the steps of providing a plurality of organic precursors in the vapor phase, and reacting the plurality or organic precursors at a sub-atmospheric pressure. Also included are thin films made by such a method and apparatuses used to conduct such a method. The method is well-suited to the formation of organic light emitting devices and other display-related technologies.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. application Ser. No.10/125,400, filed Apr. 19, 2002, which is a continuation of U.S.application Ser. No. 09/736,090, filed on Dec. 13, 2000, which is acontinuation of U.S. application Ser. No. 09/663,143, filed on Sep. 15,2000, which is a continuation of U.S. application Ser. No. 08/972,156,filed on Nov. 17, 1997, the subject matter of which are incorporated byreference herein in their entireties.

GOVERNMENT RIGHTS

[0002] This invention was made with Government support under ContractNo. F49620-92-J-05 24 (Princeton University), awarded by the U.S. AirForce OSR (Office of Scientific Research). The Government has certainrights in the invention.

FIELD OF THE INVENTION

[0003] The present invention relates to the fabrication of opticalquality thin films, and more particularly to the low pressurefabrication of such thin films for application in non-linear opticaldevices and organic light emitting devices.

BACKGROUND OF THE INVENTION

[0004] The field of organic electroluminescence is a rapidly growingtechnology. Spurred by potential application to displays, organic lightemitting devices (OLEDs) are capable of achieving external quantumefficiencies of over 3%, and operational lifetimes on the order of10,000 hours at video brightness. Both small molecule and polymer-basedOLEDs are known, but polymerbased devices have a general advantage ofsimple and inexpensive fabrication by spin-on deposition techniques. Incontrast, small molecule devices are usually fabricated by thermalevaporation in vacuum, which is usually a more expensive process thanspin-on deposition. Examples of OLED structures and processingtechniques are provided in published PCT application WO 96/19792,incorporated herein by reference.

[0005] The use of organic vapor phase deposition (OVPD) has madeprogress towards the low cost, large scale deposition of small molecularweight organic layers with numerous potential photonic deviceapplications such as displays. The OVPD process is described in U.S.Pat. No. 5,554,220 to Forrest et al.; S. R. Forrest et al., “IntenseSecond Harmonic Generation and Long-Range Structural Ordering in ThinFilms of an Organic Salt Grown by Organic Vapor Phase Deposition,” 68Appl. Phys. Lett. 1326 (1996); and P. E. Burrows et al., “Organic VaporPhase Deposition: a New Method for the Growth of Organic Thin Films withLarge Optical Non-linearities,” 156 J. of Crystal Growth 91 (1995), eachof which is incorporated herein by reference.

[0006] The OVPD process uses carrier gases to transport source materialsto a substrate, where the gases condense to form a desired thin film.The OVPD technique has been used, for example, to deposit films of theoptically non-linear organic (NLO) salt,4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST), from volatileprecursors 4′- dimethylamino-N-methyl-4-stilbazolium iodide (DASI) andmethyl p-toluensulfonate (methyltosylate, MT), which are transported bycarrier gases to a heated substrate. In this process, DASI thermallydecomposes to form 4-dimethylamino-4-stilbazole (DAS), whichsubsequently reacts with MT to form DAST on the substrate.

[0007] Because of its capability for controlled codeposition ofmaterials with radically different vapor pressures, OVPD is believed tobe the only method for the precise stoichiometric growth ofmulti-component thin films. However, the OPVD process is conducted atatmospheric pressure, and films grown at or near atmospheric pressureare often rough and have non-uniform surface morphologies due to gasphase nucleation and a diffusion-limited growth process.

SUMMARY OF THE INVENTION

[0008] The present invention makes use of low pressure depositiontechniques to produce organic thin films having superior surfaceproperties. In one aspect, the present invention comprises a method forpreparing an organic thin film on a substrate, the method comprising thesteps of providing a plurality of organic precursors, the organicprecursors being in the vapor phase; and reacting the plurality oforganic precursors at a sub-atmospheric pressure in the presence of thesubstrate to form a thin film on the substrate. In another aspect, thepresent invention includes organic films made by such a method. In yetanother aspect, the present invention includes an apparatus designed tofacilitate the reaction of organic precursors at sub-atmosphericpressures to form an organic film on a substrate.

[0009] One advantage of the present invention is that it providesmulti-component organic thin films wherein the amount of each componentin such films can be controlled accurately and precisely.

[0010] Another advantage of the present invention is that it providesuniform organic thin films having smooth surfaces.

[0011] Another advantage of the invention is that it provides a lowpressure organic vapor phase deposition method and apparatus for thegrowth of thin films of organic light emitting materials and opticallynon-linear organic salts.

[0012] Another advantage of the invention is that it provides a lowpressure organic molecular beam deposition method and apparatus for theformation of thin films of organic light emitting materials andoptically non-linear organic salts.

[0013] Yet another advantage of the invention is that it provides amethod and apparatus for the uniform deposition of organic materialsover large substrate areas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 shows a LPOVPD reactor, in accordance with an embodiment ofthe present invention.

[0015]FIG. 2 shows an OMVD reactor, in accordance with an embodiment ofthe present invention.

[0016]FIG. 3 shows an apparatus for the continuous low pressuredeposition of organic materials onto substrates, in accordance with anembodiment of the present invention.

[0017]FIGS. 4A and 4B are planar and cross-sectional views,respectively, of a reactant gas distributor, in accordance with anembodiment of the present invention.

[0018]FIG. 5 is a side view of a roll-to-roll substrate deliverymechanism, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

[0019] The present invention provides a method and apparatus for thegrowth of organic thin films on substrates while under sub-atmosphericpressures. The method of the invention is herein identified as lowpressure organic vapor deposition (LPOVPD). The LPOVPD method of thepresent invention allows for the accurate and precise control of thedeposition of multi-component organic thin films. In addition, the thinfilms of the present invention are characterized by superior surfaceproperties such as low surface roughnesses.

[0020] A LPOVPD reactor 10 in accordance with an embodiment of thepresent invention is schematically shown in FIG. 1. Reactor 10 includesa reaction chamber, such as a reactor tube 12, and tubing extending intothe reaction chamber. Reactor tube 12 is a cylinder having a suitabledimension such as, for example, a diameter of 10 cm and an approximatelength of 45 cm in an experimental apparatus. Reactor tube 12 is made ofany suitable material such as glass or quartz. An open container such ascrucible 14 contains a first organic precursor material and is placedwithin tube 36 near one end 20 of the reactor tube 12. Alternatively,crucible 14 is placed directly on the reactor tube 12 or on shelves ortubes therein. Crucible 14 is heated or cooled by means of a multi-zoneheater/cooler 18, which substantially surrounds reactor tube 12. Thetemperature control of crucible 14 results in the thermal decompositionor volatilization of the first organic precursor material withincrucible 14. A regulated stream 30 of inert carrier gas is passedthrough tube 36 and into the reaction chamber, thus causing vapor of thefirst organic precursor to flow along the reactor tube 12 toward itsexhaust end 22. The inert carrier gas is an inert gas such as nitrogen,helium, argon, krypton, xenon, neon and the like. Gases with a reducingcharacter, such as hydrogen, ammonia and methane, are also inert formany organic materials. Use of these reducing gases often has theadditional benefit of assisting in the burning of undesired excessreactants.

[0021] Inert gas is delivered from tank 24 through a regulator valve 26and into tubing 28 for delivery through at least two flow paths, 30 and38, and into reactor tube 12. One flow path 30 includes a seriesconnected pressure regulator 32, flow meter 34 and quick switching valve35 from which the carrier gas is delivered into end 20 of reactor tube12. The second flow path 38 includes a series connected pressureregulator 40, flow meter 42 and quick switching valve 39 from which thecarrier gas flows into a bubbler 46, which contains a second organicprecursor material 48. To facilitate the temperature control of secondorganic precursor material 48, bubbler 46 is partially immersed in bath50 within container 52. Inert gas from tank 24 bubbles through thesecond organic precursor 48 and through tubing 54 to carry vapor of thesecond organic precursor 48 into reactor tube 12. During this process,tube 54 must be maintained at a sufficiently high temperature to avoidrecondensation of the volatilized second organic precursor 48 as ittravels from the bubbler to the reactor.

[0022] The amount of any precursor entering reactor tube 12 iscontrolled by processing parameters such as the temperature and flowrate of the carrier gas and the temperature of the reactants. The LPOVPDmethod provides precise metering of the precursors or reactantsindependently of their vapor pressure or chemical nature using pressuremass flow controllers. The present method thus permits the combinationof materials with widely different characteristics in ratios necessaryfor the production of desired films.

[0023] The precursor streams are capable of being turned on and offalmost instantly by employing quick switching valves 35 and 39. Thesevalves direct the precursor streams into reactor 12 or into a by-passline (not shown), so that at any given time, different precursor streamsmay be entering the reactor 12 for the deposition of films of differentcompositions and characteristics. Valve 39 also regulates the admittanceof carrier gas into bubbler 46. Valves 35 and 39 thus allow the rapidchange of reactant streams entering the reactor 12, for changing thenature and the composition of the grown films. It is thus possible, forexample, to grow ABAB, ABCABC, ABABCAB, and ABCDABCD-type films, whereeach letter denotes a different molecular layer or composition.

[0024] A vacuum pump 66 and control throttle valve 68 are attached toreactor 10 at the exhaust 62. Most of the organic vapors not depositedonto substrate 58 are condensed in a trap 64 placed upstream from pump66. Trap 64 contains liquid nitrogen or a neutral, fluorocarbon oil, forexample. Throttle valve 68 regulates the pressure in reactor 10. Anappropriate pressure gauge is connected to the reactor (not shown) withelectronic feedback to the control throttle valve 68 to maintain adesired pressure in the reactor.

[0025] Vacuum pump 66 provides a pressure of about 0.001-100 Torr inreactor tube 12. The actual pressure for any combination of acceptor,donor, and single component layers is experimentally determined withreference to the temperatures required to volatilize the precursormaterials, the wall temperature to prevent condensation of the precursormaterials, and the reaction zone temperature gradient. The optimalchoice of pressure is unique to the requirements of each depositedorganic layer. For example, optimal pressures for the deposition ofsingle component layers such as tris-(8-hydroxyquinoline) aluminum(Alq₃) or N-N′-diphenyl-N,N-bis(3-methylphenyl)1,1′-biphenyl-4,4′diamine (TPD) are about 0.1-10 Torr.

[0026] the substrates on which the thin films of the present inventionare deposited are typically selected from those materials that arecommonly encountered in semiconductor and optics manufacturing. Suchmaterials include, for example, glass, quartz, silicon, gallium arsenideand other III-V semiconductors, aluminum, gold and other precious andnon-precious metals, polymer films, silicon dioxide and silicon nitride,indium-tin-oxide and the like. For high quality optical thin films, itis preferable to use substrates that provide crystalline interactionswith the deposited organic film to induce epitaxial growth. To achievesuch epitaxial growth, it is often necessary to coat substrates withnon-polar organics having crystalline structures similar to the film tobe deposited.

[0027] In addition, as an organic thin film is deposited onto substrate58, it is often desirable to control the temperature of the substrate.Independent control of substrate temperature is accomplished, forexample, by contacting substrate 58 with temperature-control block 60,which has channels therein for the circulation of materials such aswater, gas, freon glycerin, liquid nitrogen, and the like. It can alsobe heated by the use of resistance or radiant heaters positioned on ornear the block 60.

[0028] Reactor 20 of FIG. 1 is expandable to include multiple bubblers46N to feed additional precursors into reactor 20. Similarly, multiplecarrier gas flow paths 30N are used to deliver yet additional precursorsfrom crucibles 14N. As an alternative, crucibles 14, 14N are verticallystackable on shelves or in tubes within reactor tube 12 for processingthe additional precursors. Depending on the organic film to bedeposited, one or more flow paths 30, 38 are used alone or in anycombination to provide the necessary precursor materials.

[0029] The method of the present invention is used to deposit a widevariety of organic thin films from the reaction of vapor precursors. Asused herein, “reaction” refers to a chemical reaction in which precursorreactants form a distinct reaction product, or alternatively, it merelyrefers to a combination or mixture of precursor materials, or whereprecursor materials form a donor-acceptor or guest-host relationship.For example, in accordance with the present invention, the following NLOmaterials are formed as thin films by the reaction of the listedprecursors: Film Material First Precursor Second Precursor4′-dimethylamino-N- 4′-dimethylamino-4- methyl tosylate (MT)methyl-4-stilbazolium stilbazole (DAS) tosylate (DAST)4′-dimethylamino-4- methyl 4′-dimethylamino-4- methylstilbazoliummethanesulfonate stilbazole (DAS) methanesulfonate (MM) (DASM)4′-dimethylamino-4- methyl 4′-dimethylamino-4- methylstilbazoliumtrifluoromethanesulfo stilbazole (DAS) trifluoromethanesulfo nate(M_(f)M) nate (DASM_(f)) 4′-dimethylamino-N- methyl tosylate (MT)4′-dimethylamino-4- methyl-4-stilbazolium methylstilbazolium tosylate(DAST) thiophenoxide (DASTh) 4′-methoxy-4- methyl tosylate (MT)4′-methoxy-4- methylstilbazolium methylstilbazole tosylate (MeOST)(MeOS) 4′-dimethylamino-N- methyl tosylate (MT) 4′-dimethylamino-4-methyl-4-stilbazolium ethylstilbazolium tosylate (DAST) iodide (DAS (Et)I) 4′-dimethylamino-N- methyl tosylate (MT) 4′-dimethylamino-4-methyl-4-stilbazolium ethylstilbazolium tosylate (DAST) hydroxide (DAS(Et) OH) 4′-dimethylamino-4- acetyl 4′-dimethylamino-4-acetylstilbazolium toluenesulfonate (AT) stilbazole (DAS) tosylate(DAAST) 4′dimethylamino-4- methyl 4′-dimethylamino-4- methylstilbazoliumtrifluoroacetate stilbazole (DAS) trifluoroacetate (MA_(f)) (DASA_(f))

[0030] In another example relating more specifically to light emittingmaterials used to make OLEDs, the precursors consist of, for example,tetrathisferlvalene (TFF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ).The mixing step results in the charge transfer complex TTF-TCNQ whichdeposits onto a substrate. In another example relating to OLEDs,4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM)is added into a high flow rate carrier gas stream while Alq₃ is addedinto a lower flow rate carrier gas stream. These streams are then mixedin a central reactor tube, thus providing the desired dilution of theguest molecule in the host matrix film to form a single luminescentlayer. Other guest molecule examples in Alq₃, hosts are5,10,15,20-tetraphenyl-21H, 23H-porphine (TPP), Rubrene, DCM2, Coumarin,etc. As a variation, multiple dopants can be added into a single host toachieve efficient broad color conversion.

[0031] In another example, a bilayer light emitting device consisting ofa hole transporting layer (“HTL”) such as TPD;α-4,4′-bis[N-(1-naphthyl)-N-Phenyl-amino]biphenyl(α-NPD); or MTDATA,layered onto the surface of a light emitting layer (“EL”) such as Alq₃,bis-(8hydroxyquinoline) aluminum oxyphenyl ((Alq₃)′-(OPh) or dopedcombinations of these layers, is grown by sequentially growing the HTLand EL to desired thicknesses. This is followed by growing additionallayers onto the organics, or by growth on metallic contact layers usingorganometallic sources such as trimethyl-indium, trimethyl-gallium, andthe like.

[0032] In addition to the apparatus and method described with referenceto FIG. 1, the present invention includes a low pressure reactor 70 andmethod as shown in FIG. 2. Reactor 70 includes a modified ultra-highvacuum chamber 71 and a vacuum pump such as a turbomolecular pump (notshown) connected to valve 72. Typical chamber base pressures in chamber71 are 10⁻⁸-10⁻¹¹ Torr. The process of depositing organic layers withthe use of reactor 70 is called organic molecular beam vapor deposition(OMVD). Although both LPOVPD and OMVD make use of sub-atomosphericpressures for the deposition of organic layers, the principle differencebetween these processes is that in the latter, the molecular mean freepath is comparable to or larger than the dimensions of the chamber 70.In comparison, the mean free path in LPOVPD is significantly shorterthan the gas reactor dimensions. OMVD thus allows for the formation ofhighly directed molecular “beams” from the injectors to the substrate,allowing for precise kinetic control of the grown film thickness, purityand morphology.

[0033] Bubbler 74 is included for containing a first precursor material75. The bubbler 74 is placed into, container 76 and immersed in atemperature controlled bath 80. A high purity inert carrier gas 78bubbles through first precursor 75, and carries respective vaporsthrough heated tubing 79 and into vacuum chamber 71 by way of injector82. Once inside chamber 71, the precursor vapors form a molecular beam83 that impinges on substrate 85. Substrate 85 is provided with a meansfor providing temperature control such as coolant port 81, for example.

[0034] Vacuum chamber 71 optionally is provided with at least oneKnudsen or K-cell 86, which contains a second precursor material 88.K-cell 86 is a uniformly heated and controlled oven for the effusion ofevaporants under vacuum. For example, K-cell 86 is heated to crack DASIor other precursor and sublime the resulting DAS, such that it isinjected into reactor 70 as a molecular beam 89. Alternatively, K-cell86 simply sublimes a single component substance such as Alq₃.Alternatively, K-cell 86 is fitted with a carrier gas inlet used todilute the concentration of the molecular species being sublimed orevaporated into the gas stream by thermalization. This dilution processis particularly useful in achieving precise doping levels of guest-hostsystems such as DCM-Alq₃ by controlling the temperatures of bath 80 andKnudsen cell 86 as well as the flow of carrier gas 78 to bubbler 74.

[0035] Molecular beams 83 and 89 impinge on substrate 85 to deposit anorganic thin film, the thickness of which is monitored by quartz crystal93. Sample holder 90 rotates to ensure a uniform deposition and reactionof precursor materials. The deposition of precursor materials is furthercontrolled by shutters 87, which are used to interrupt molecular beams83 and 89.

[0036] Reactor 70 also optionally includes a cooled shroud 91 to helpkeep the pressure of vacuum chamber 71 to a minimum for re-evaporatedprecursor materials. Also preferably included is a partition 92 to keepprecursor materials from migrating and thus contaminating each other.

[0037] Reactor 70 is embellished with many of the same attributes of theLPOVPD reactor shown in FIG. 1, such as quick switching valves, bypasslines and the like. Reactor 70 is able to be fitted with multipleKnudsen cells and bubblers for the deposition of multiple precursormaterials onto substrate 85. Reactor 70 also preferably includes a“load-lock” 94 for sample introduction. Load-lock 94 includes door 95and vacuum pump 96, and provides for the exchange of samples withoutcompromising the pressure of chamber 71.

[0038] The apparatus of FIG. 1 is optionally modified for the continuousdeposition of organic layers on large area substrates, as shown by theexample illustrated in FIG. 3. The apparatus of FIG. 3 includes aplurality of vacuum chambers such as loading chamber 146, organic layerdeposition chambers 150 and 152, contact deposition chamber 154, andunload chamber 156. As an example, each deposition chamber is a LPOVPDreactor 10 of FIG. 1. The substrates 137 are transported on a conveyorbelt 148 through each of chambers 150, 152, 154 and 156. In theembodiment shown in FIG. 3, chambers 150, 152 and 154 include sources158, 160 and 162, respectively, of radiant heat to prevent thecondensation of organic vapors. Although only two organic layerdeposition chambers 150 and 152 are shown in FIG. 3, additional chambersare included as desired. In passing from the loading chamber 146 to theorganic layer deposition chambers 150 and 152, and from the contactdeposition chamber 154 to the unload chamber 156, the substrate 137passes through air locks (not shown) so as not to compromise the vacuumin the chambers 150, 152, and 154. As an example relating to OLEDs,chambers 150 and 152 are used for the deposition of TPD and Alq₃,respectively, and chamber 154 is used for the deposition of an Mg:Agcontact layer.

[0039] Each of the chambers 150, 152, an 154 in the example of FIG. 3includes a reactant gas distributor (RGD) 108 for the deposition oforganic precursor materials, as shown in detail in FIGS. 4A and 4B.RGD's 108 are used as an alternative to the organic precursor deliverymechanisms of FIGS. 1 and 2, and are used to provide gas curtains, 120,120′, 120″ and 120′″. RGD 108 ensures that where multiple organicprecursors are deposited, the precursors remain separated untildeposited on a substrate, whereupon reaction of the precursors ispermitted to take place. RGD 108 includes heater 122, second carrier gasinlet 112 and gas manifold 132. Heater 122 prevents the prematurecondensation of organic precursor materials. Over RGD 108 is a firstcarrier gas inlet 114 and distributor plate 110. First carrier gas inlet114 supplies gas which usually carries a first organic precursor ofgenerally low volatility such as, for example, MT. The first carrier gasenters a reaction chamber though distributor plate 110, which is a wiremesh, a glass filter material, or a porous stainless steel plate, forexample. The column of carrier gas flowing through distributor plate 110is shadowed by the RGD 108. RGD 108 provides a planar gas curtain 120 ofa second organic precursor of generally low vapor pressure such as, forexample, DAS. A second carrier gas containing a second organic precursorenters at inlet 112 and is directed into gas manifold 132. Manifold 132is a hollow tube having a line of holes 134 for feeding the secondcarrier has into an annular cavity 126, which surrounds manifold 132.Second carrier gas exits RGD 108 through slit 136, thus giving it theshape of a planar curtain.

[0040] As an example, curtain 120 is comprised of TPD vapors, curtain120′ is comprised of Alq₃ vapors and curtain 120″ is comprised of vaporssuch as a polypyrole or metallorganic compounds that produce aconductive surface. If desired, control or tuning of the color of lightemitted by an OLED can be effected by suitable doping of the Alq₃ layerwith an additional RGD device 108 in the chamber 152 that produces acurtain 120′″ of dopant vapor.

[0041] The apparatus of FIG. 1, FIG. 2 or FIG. 3 is optionally modifiedby using a “roll-to-roll” substrate delivery system, as shown in FIG. 5.The delivery system shown in FIG. 5 is suitable for the deposition oforganic thin films onto large area, flexible substrates. Substrate 180is made of a polymer sheet or metal foil, for example, and is deliveredfrom roll 181 to roll 182. The deposition of organic precursors ontosubstrate 180 occurs when substrate 180 is unrolled from roll 181 and istherefore exposed to the reaction chamber of FIG. 1, or when exposed tothe molecular beam or curtains of FIGS. 2 and 3, respectively. Rolls 181and 182 are driven by any suitable means, such as a variable speedmotor. The speed at which substrate 180 is passed from roll 181 to roll182 dictates the thickness of the organic film that forms on substrate180.

[0042] The present invention is further described with reference to thefollowing non-limiting examples.

Example 1

[0043] Using the apparatus of FIG. 1, layers of organic light emittingmaterials were grown using glass and flexible polyester substratesprecoated with transparent layers of indium tin oxide (ITO). The ITOforms the anode of the device with a thickness of 1700 Å and 1200 Å forthe glass and polyester substrates, respectively, yielding anoderesistances of 10 Ω and 60 Ω, respectively. Glass substrates werecleaned by rinsing in a solution of detergent and deionized water in anultrasonic bath, and then boiling in 1,1,1-tri.chloroethane, rinsing inacetone and finally rinsing in 2-propanol. To avoid damage due toexposure to organic solvents, the flexible substrates were cleaned byrinsing only in the detergent and 2-propanol solutions.

[0044] Glass substrates were placed within the reactor tube 12 at alocation where the temperature was approximately 220° C. The first layerdeposited on the ITO surface was TPD, a hole transporting material.Specifically, TPD vapor was carried from crucible 14 to substrate 28 vianitrogen carrier gas. The TPD growth conditions included a sourcetemperature of 200±5° C., a nitrogen carrier gas flow rate of 100 sccm,a reactor pressure of 0.50 Torr and a growth time of 20 minutes. At anitrogen flow rate of 100 sccm, the Reynolds number of the system was˜500, indicating operation well within the laminar flow regime. The TPDlayer was grown to a thickness of between 100-300 Å.

[0045] After deposition, the temperature near the TPD crucible wasreduced, and the corresponding nitrogen flow was shut off. Next, anelectron transporting layer of Alq₃ was grown by turning on a separatenitrogen line to carry Alq₃ vapor from crucible 14N into chamber 12. TheAlq₃ growth conditions included a source temperature of 247±8° C., anitrogen flow rate of 50 sccm, a pressure of 0.65 Torr and a growth timeof 10 minutes. During the deposition of both the TDP and Alq₃, thesubstrate was maintained at 15° C. using a water cooled stainless steelsubstrate holder. The TPD layer was grown to a thickness of between700-1100 Å.

[0046] After deposition of the Alq₃ layer, the substrate was removedfrom the reactor and a Mg:Ag top contact was applied by thermalevaporation. The contact was completed with the evaporation of a 1000 Åthick protective Ag layer.

[0047] The use of low pressures during deposition resulted in organiclayers having smooth and uniform surfaces. For example, the TPD and Alq₃layers were measured via atomic force microscopy to have RMS roughnessesof 6-8 Å and 9-11 Å, respectively. The resulting OLED devices exhibitedcurrent-voltage characteristics wherein I∞V at low voltages and I∞V⁹ athigher voltages. The turn-on voltage, V_(T), at which the power lawdependence of I on V changed, was about 6V.

Example 2

[0048] An NLO film was prepared using the apparatus shown in FIG. 1. MT48 was loaded into a 30 cm³ bubbler 46, the temperature of which wasmaintained at approximately 80°-100° C. by silicone oil bath 50.Nitrogen gas was used to bubble through the MT 48, thereby carrying MTvapor through glass tube 54 and into reactor tube 12 at a locationapproximately 5 cm beyond crucible 14, which contained was placed on thefloor of reactor tube 12 and DASI. The pressure within reactor tube 12was maintained at about 10⁻² torr. DAS vapor reacted with the MT vaporto form a solid film of DAST on substrates 58, which were supported onsubstrate block 60. Excess unreacted MT vapor and any volatileside-reaction products were exhausted from exhaust tube 62. DAST filmsthus formed are useful as optical switches, for example.

[0049] The present invention makes use of low pressure depositiontechniques to produce organic thin films having superior surfaceproperties and accurate and precise compositions. Although variousembodiments of the invention are shown and described herein, they arenot meant to be limiting. For example, those of skill in the art mayrecognize certain modifications to these embodiments, whichmodifications are meant to be covered by the spirit and scope of theappended claims.

[0050] The subject invention as disclosed herein may be used inconjunction with co-pending applications: “High Reliability, HighEfficiency, Integratable Organic Light Emitting Devices and Methods ofProducing Same”, Ser. No. 08/774,119 (filed Dec. 23, 1996), now U.S.Pat. No. 6,046,543; “Novel Materials for Multicolor LED's”, Ser. No.08/850,264 (filed May 2, 1997), now U.S. Pat. No. 6,045,930; “ElectronTransporting and Light Emitting Layers Based on Organic Free Radicals”,Ser. No. 08/774,120 (filed Dec. 23, 1996), now U.S. Pat. No. 5,811,833;“Multicolor Display Devices”, Ser. No. 08/772,333 (filed Dec. 23, 1996),now U.S. Pat. No. 6,013,982; “Red-Emitting Organic Light EmittingDevices (LED's)”, Ser. No. 08/774,087 (filed Dec. 23, 1996), now U.S.Pat. No. 6,048,630; “Driving Circuit For Stacked Organic Light EmittingDevices”, Ser. No. 08/792,050 (filed Feb. 3, 1997), now U.S. Pat. No.5,757,139; “High Efficiency Organic Light Emitting Device Structures”,Serial No. 08/772,332 (filed Dec. 23, 1996), now U.S. Pat. No.5,834,893; “Vacuum Deposited, Non-Polymeric Flexible Organic LightEmitting Devices”, Serial No. 08/789,319 (filed Jan. 23, 1997), now U.S.Pat. No. 5,844,363; “Displays Having Mesa Pixel Configuration”, Ser. No.08/794,595 (filed Feb. 3, 1997), now U.S. Pat. No. 6,091,195; “StackedOrganic Light Emitting Devices”, Serial No. 08/792,046 (filed Feb. 3,1997), now U.S. Pat. No. 5,917,280; “High Contrast Transparent OrganicLight Emitting Device Display”, Serial No. 08/821,380 (filed Mar. 20,1997), now U.S. Pat. No. 5,986,401; “Organic Light Emitting DevicesContaining A Metal Complex of 5-Hydroxy-Quinoxaline as a Host Material”,Ser. No. 08/838,099 (filed Apr. 15, 1997), now U.S. Pat. No. 5,861,219;“Light Emitting Devices Having High Brightness”, Ser. No. 08/844,353(filed Apr. 18, 1997), now U.S. Pat. No. 6,125,226; “OrganicSemiconductor Laser”, Ser. No. 60/046,061 (filed May 9, 1997), “OrganicSemiconductor Laser”, Ser. No. 08/859,468 (filed May 19, 1997), now U.S.Pat. No. 6,111,902; “Saturated Full Color Stacked Organic Light EmittingDevices”, Serial No. 08/858,994 (filed May 20, 1997), now U.S. Pat. No.5,932,895 ; “An Organic Light Emitting Device Containing a HoleInjection Enhancement Layer”, Ser. No. 08/865,491 (filed May 29, 1997),now U.S. Pat. No. 5,998,803; “Plasma Treatment of Conductive Layers”,Ser. No. PCT/US97/10252; (filed Jun. 12, 1997), now U.S. national phaseapplication number 09/202,152, filed May 5, 1999; “Patterning of ThinFilms for the Fabrication of Organic Multi-Color Displays”, Ser. No.PCT/US97/10289 (filed Jun. 12, 1997), now U.S. national phaseapplication number 09/202,152, filed Jun. 14, 1999; ”“DoubleHeterostructure Infrared and Vertical Cavity Surface Emitting OrganicLasers”, Serial No. 60/053,176 (filed Jul. 18, 1997), now U.S. Pat. No.5,874,803; “Oleds Containing Thermally Stable Asymmetric Charge CarrierMaterials”, Ser. No. 08/929,029 filed (Sep. 8, 1997), “Light EmittingDevice with Stack of Oleds and Phosphor Downconverter”, Ser. No.08/925,403 (filed Sep. 9, 1997), now U.S. Pat. No. 5,874,803, “AnImproved Method for Depositing Indium Tin Oxide Layers in Organic LightEmitting Devices”, Ser. No. 08/928,800 (filed Sep. 12, 1997), now U.S.Pat. No. 5,981,306, “Azlactone-Related Dopants in the Emissive Layer ofan Oled” (filed Oct. 9, 1997), Ser. No. 08/948,130, “A HighlyTransparent Organic Light Emitting Device Employing A Non-MetallicCathode”, (filed Nov. 3, 1997), now U.S. Pat. No. 6,030,715, AttorneyDocket No. 10020/40 (Provisional), now U.S. Provisional Application No.60/064,005, and “A Highly Transparent Organic Light Emitting DeviceEmploying a Non Metallic Cathode”, (filed Nov. 5, 1997), Attorney DocketNo. 10020/44, now U.S. Ser. No. 08/964,863, each co-pending applicationbeing incorporated herein by reference in its entirety. The subjectinvention may also be used in conjunction with the subject matter ofeach of co-pending U.S. patent application Ser. No. 08/354,674, now U.S.Pat. Nos. 5,707,745, 08/613,207, now U.S. Pat. Nos. 5,703,436,08/632,322, now U.S. Pat. Nos. 5,757,026 and 08/693,359 and provisionalpatent application Ser. No. 60/010,013, to which non-provisional U.S.application Ser. No. 08/779,141 filed Jan. 6, 1997 claimed benefit, nowU.S. Pat. Nos. 5,986,268; 60/024,001, to which non-provisional U.S.application No. 08/789,319 filed Jan. 23, 1997 claimed benefit, now U.S.Pat. Nos. 5,844,363 and 60/025,501, to which non-provisional U.S.application No. 08/844,353 filed Apr. 18, 1997 claimed benefit, now U.S.Patent No. 6,125,226, each of which is also incorporated herein byreference in its entirety.

What is claimed is:
 1. An apparatus for the physical vapor deposition ofa film comprising an organic small molecule material on a substrate,said apparatus comprising: (a) a deposition chamber; (b) at least oneflow path in fluid communication with said deposition chamber, said flowpath comprising: (i) a carrier gas source, (ii) an organic smallmolecule material source, and (iii) a flow controller; (c) a substrateholder disposed within said deposition chamber; and (d) a vacuum pump influid communication with said deposition chamber and adapted to providea pressure ranging from 0.001 torr to 100 torr within said depositionchamber; wherein the deposition chamber has walls that may be heated toa temperature sufficiently high to avoid recondensation of volatilizedorganic precursor, without decomposing the volatilized organicprecursor.
 2. The apparatus of claim 1, wherein said flow controllerincludes a pressure regulator.
 3. The apparatus of claim 1, wherein saidflow controller includes a flow meter.
 4. The apparatus of claim 1,wherein said flow controller includes a switching valve.
 5. Theapparatus of claim 1, wherein said deposition chamber has heated walls.6. The apparatus of claim 1, wherein said deposition chamber is providedwith one or more radiant heat sources.
 7. The apparatus of claim 1,further comprising a heater substantially surrounding said depositionchamber.
 8. The apparatus of claim 7, wherein said heater is amulti-zone heater/cooler.
 9. The apparatus of claim 1, wherein thesubstrate holder is cooled.
 10. The apparatus of claim 9, wherein thesubstrate holder comprises a temperature-control block.
 11. Theapparatus of claim 1, wherein said organic small molecule materialsource is an open container holding said organic small moleculematerial.
 12. The apparatus of claim 11, wherein said open container isheated.
 13. The apparatus of claim 1, wherein said apparatus comprisestwo or more flow paths.
 14. An apparatus for physical vapor depositionof a film comprising an organic small molecule material on a substrate,said apparatus comprising: a deposition chamber; means for heating saiddeposition chamber; means for introducing vapors of organic smallmolecule materials into said deposition chamber; means for cooling asubstrate within said deposition chamber; and means for maintaining thepressure in said reaction chamber at a pressure ranging from 0.001 torrto 100 torr; means for heating the deposition chamber walls to atemperature sufficiently high to avoid recondensation of vapors of theorganic small molecule materials, without decomposing the organic smallmolecule materials.